Heretofore, in supplying cops to each magazine mounted in juxtaposition to each winding unit of an automatic thread winder, it has been necessary for an operator to make the round of the winder to watch for any magazine devoid of cops and to perform a series of manual operations of supplying cops one by one to such magazine, taking out the yarn end and holding it on a yarn clamp. Such manual operations require much trouble and the labor cost runs up, and hence, such manual operations have proved to be a great hindrance to full automation of the winder operation.